CN114826182A

CN114826182A - Method for producing a piezoelectric resonator and piezoelectric resonator

Info

Publication number: CN114826182A
Application number: CN202210070231.4A
Authority: CN
Inventors: F·霍伊克; M·普里茨乔; M·库恩克; P·施莫尔格鲁贝尔; R·萨莫拉; S·卢瓦索; S·马约尼; S·克劳泽; V·莫罗索夫
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2021-01-21
Filing date: 2022-01-21
Publication date: 2022-07-29
Also published as: US20220231652A1; DE102021200518B3; TW202236708A

Abstract

A method for producing a piezoelectric resonator is proposed, in which a vibratable structure is formed from a highly doped silicon functional layer, having the following steps: depositing a piezoelectric layer and forming a recess in the lateral region in such a way that the silicon functional layer is exposed in the recess, a silicide layer being formed on the surface of the silicon functional layer exposed in the recess. Forming a diffusion barrier layer on the silicide layer, depositing and structuring the first and second metallization layers such that a feed line and two connection elements are formed, forming a vibratable structure by the structured silicon functional layer, wherein the silicon functional layer of the vibratable structure is electrically contactable by the first connection element and forms a lower electrode of the resonator, wherein the first metallization layer of the vibratable structure is electrically contactable by the second connection element and forms an upper electrode of the resonator.

Description

Method for producing a piezoelectric resonator and piezoelectric resonator

Technical Field

The invention is based on a method for producing a piezoelectric resonator, wherein the vibratable structure of the resonator is formed by a highly doped silicon functional layer, wherein the silicon functional layer is arranged above a substrate with respect to the vertical direction and has a transverse main extension surface with a first transverse region, a second transverse region and a third transverse region, wherein a cavity is arranged in the first transverse region below the silicon functional layer.

Background

Silicon-based piezoelectric MEMS resonators offer the advantage of being manufacturable as an integrated component of a silicon chip, in addition to high resonance sharpness and small form factor (Formfaktor). The actuators which produce the conversion of the electrical signal into mechanical vibrations are usually piezoelectric layers which are arranged as part of a sandwich between two electrodes and are elastically deformed by the field generated by the electrodes.

Such silicon resonators are known, for example, from the publication of the Experimental study of the effects of size variations on piezoelectric transformed MEMS resonators by Jaakkola et al (IEEE International frequency control workshop, New harbor beach, Calif., 2010, page 410-. The resonator studied here consists of a square plate made of highly p-doped monocrystalline silicon, which is bound to the substrate at the corners with flexible anchors (Ankern). The electromechanical coupling is obtained by a layer made of aluminum nitride (AlN) deposited on the plate. The molybdenum layer arranged on the piezoelectric layer functions here as the upper electrode, while the lower electrode is formed by the silicon plate itself. By means of corresponding contacting of the electrodes, an alternating electric field can be applied at the AlN layer, by means of which different vibration modes of the resonator can be excited, the shape and frequency of which are determined substantially by the geometry of the resonator and in particular by the lateral dimensions of the resonator.

Disclosure of Invention

On this background, it is an object of the present invention to provide a cost-effective MEMS process for high-performance and miniaturized resonators having a piezoelectric functional layer.

Compared to the prior art, the method according to the invention allows a cost-effective, highly parallel MEMS process to be implemented, by means of which a maximum overlap of the piezoelectric layer and the two electrodes and thus a maximum electromechanical efficiency of the resonator can be achieved, wherein at the same time a high conductivity of the wire-bondable connecting elements and the feed lines is ensured. In this case, the two soft metallization layers, with high conductivity, on the resonator do not lead to hardening, nor to mechanical tensioning or tensioning with a pronounced temperature dependence. Furthermore, the following resonators are obtained by this method: the piezoelectric layer of the resonator has a very low scattering in terms of layer thickness and the resonator shows very little structural change overall from component to component.

The multilayer system produced and structured by the method according to the invention (strukturrieren) initially has at least one highly doped, in particular p-doped, silicon functional layer which is arranged parallel to the substrate wafer. The lateral direction (i.e. the direction extending parallel to the main extension plane) and the direction extending perpendicular to the main extension plane, which is also referred to as the vertical direction in the following, are determined by the main extension plane of the silicon functional layer or substrate. The extension of the layers in the vertical direction is referred to as the thickness, and the relative positions of the layers are referred to as "upper" and "lower". The forming steps of the method according to the invention are carried out in first, second and third transverse zones, which respectively differ from each other or are spaced apart from each other in the transverse direction. The vibratable structure of the resonator is formed in the first lateral region, the connection for the lower electrode is formed in the second region, and the connection for the upper electrode is formed in the third region. The first connecting element in the second region is connected here via a recess in the piezoelectric layer to the silicon layer located thereunder, which in turn is connected via an anchor (Verankerung) of the vibratable structure to the silicon layer of this structure, which in this way acts as the lower electrode. The second connecting element in the third region is connected via a feed line to a first metallization layer on the vibratable structure, so that said first metallization layer can be contacted by the second connecting element and forms an electrode for the upper part of the piezoelectric layer. It is also conceivable for the piezoelectric layer to have two or more recesses, which may be configured in particular similarly to the first recess.

In the first region, a cavity is arranged below the silicon functional layer, which cavity can be formed in particular by etching the substrate or the sacrificial layer. In particular, material is removed here under the entire surface of the first lateral region, so that this region is exposed to the bottom. In the second and third regions, at least one dielectric layer is preferably arranged between the substrate and the silicon functional layer, which at least one dielectric layer electrically insulates the two layers from one another and/or which at least one dielectric layer serves as an etch mask for the cavity.

After the piezoelectric layer is deposited, a sacrificial layer, in particular a sacrificial layer made of silicon oxide, is deposited. Collecting (aufgefangen) by sacrificial layer necessary over-etching of metallization layer of contact in sacrificial layer

So that no material degradation of the piezoelectric layer occurs which would lead to an unfavorable change in the layer thickness. The sacrificial layer made of oxide can be removed in particular by vapor-phase hydrofluoric acid etching, by chemical-physical dry etching or by etching with aqueous hydrofluoric acid. Then at the sacrificeRecesses are formed in the layer and the piezoelectric layer, through which recesses the silicon functional layer is exposed on the inner faces (contact holes) of the recesses. To increase the electrical contact between the silicon layer and the subsequently deposited metallization layer, a silicide layer is first formed. To prevent diffusion of metal into the silicon layer, a diffusion inhibiting layer is deposited after silicide formation. The targeted removal of the silicide layer and the barrier layer around the recess (Barriere-Schicht) is preferred, since it involves a hard, mechanically strained layer, which is not allowed to appear on the resonator structure. Two metallization layers are then deposited. The first and second metallization layers may here consist, for example, predominantly, substantially or completely of gold, respectively. The second metallization layer is in particular thicker than the first metallization layer.

In the subsequent structuring of the first lateral region, by means of which the vibratable structure is exposed with respect to the lateral direction, in particular one, two or more anchors are also formed, by means of which the silicon layer of the vibratable structure is connected to the silicon layer of the second region and preferably also to the silicon layer of the third region. In the resonator produced by means of the method according to the invention, the silicon functional layer of the vibratable structure fulfils a dual function. On the one hand, it forms a vibrating body for exciting the resonator mode, and on the other hand, it acts as an electrode in the lower part of the piezoelectric layer arranged on the silicon layer.

Advantageous embodiments and embodiments of the invention result from the following description with reference to the drawings.

According to a preferred embodiment, the piezoelectric layer comprises aluminum nitride. According to another embodiment, the silicide layer has platinum and nickel. According to another embodiment, the diffusion barrier layer has tantalum and tantalum nitride. According to a further preferred embodiment, the first and second metallization layers (7, 8) comprise gold, wherein the first metallization layer (7) is composed in particular of a layer sequence of a thin tantalum layer, a platinum layer, a gold layer, a further platinum layer and a further thin tantalum layer, and wherein the second metallization layer (8) is composed in particular of a layer sequence of a tantalum layer and a gold layer. The silicide layer is preferably formed in a combination of platinum and nickel. Both materials are good silicide formers (Silizidbildner) and nickel has, in addition, excellent adhesion not only to the oxide surface but also to the AlN sidewalls of the recess. For the special requirements for metal-silicon contacts, the material combinations described above, which are specifically matched to one another, have proven to be optimal for the silicide layer and the barrier layer. By the combination according to the invention, a good electrical contact is created and an effective suppression of gold diffusion is achieved, a good adhesion to the oxide and a low layer thickness is obtained. Furthermore, in subsequent processes (e.g. wafer bonding), an excellent stability of the electrical contacts and of the barrier against thermal stress is obtained. The silicide layer can have platinum nickel silicide (NiPtSi) or consist of platinum nickel silicide. Preferably, the barrier layer is composed of tantalum and tantalum nitride. Preferably, the first metallization layer consists of a layer sequence of tantalum/platinum/gold/platinum/tantalum. The two thin tantalum layers are here adhesion layers to the underlying aluminum nitride and to the layers lying above it (in particular the first mask layer). The second metallization layer preferably consists of a layer of (Lage) tantalum followed by a thick gold layer.

According to a preferred embodiment, before the deposition of the piezoelectric layer, oxide regions of the silicon functional layer are formed in the third lateral region, wherein the second connecting elements are formed above the oxide regions in such a way that the second connecting elements are shielded downward by the oxide regions. In this way, the oxide sub-region causes an advantageous reduction or suppression of the parasitic capacitance.

Preferably, the oxide region is formed by: the silicon functional layer is isotropically etched and thermally oxidized, and the oxidized silicon functional layer is wet-chemically structured in such a way that the surfaces of the oxide partial regions and the surfaces of the non-oxide partial regions extend flush. After the formation of the oxide, the oxide is wet-chemically structured in such a way that it remains only in the recesses formed. The interaction of the silicon etch depth and the oxide thickness is preferably selected such that the center of the subsequently formed second connection element is flush with the surface of the silicon layer. In this case, the mask, the interaction of the isotropic silicon etch and the oxide etch and the etching-down of the oxide mask

Preferably, it is selected such that only a minimal surface shape (topographee) remains at the transition between silicon and oxide. With such an overhead for surface shape minimization, it is advantageously achieved that: creating as flat a surface as possible for the critical lithography technique of resonator structuring.

According to a preferred embodiment, the first and second metallization layers are deposited and structured in the first lateral region in such a way that the first metallization layer completely covers the surface of the piezoelectric layer, and the second metallization layer is structured in such a way that it covers one sub-region of the first metallization layer and does not cover another sub-region of the first metallization layer. The sub-region covered by the second metallization layer significantly increases the conductivity of the arrangement formed by the first and second metallization layers. Preferably, the second metallization layer is arranged on the vibratable structure only in those regions which are relatively unimportant to the vibration behavior. However, it is also conceivable for additional mass occupation (Massenbelegung) and/or local stiffening of the resonator to be produced by these elements, by means of which, for example, undesired vibration modes can be suppressed.

According to a preferred embodiment, the structuring of the second metallization layer is performed by: depositing a first mask layer, carrying out chemical-physical dry etching on the first mask layer, wherein the first mask layer is only partially ablated in the vertical direction, and etching the first mask layer, wherein the first mask layer is completely ablated in the vertical direction, wherein the etching of the first mask layer is carried out by hydrofluoric acid gas phase etching, chemical-physical dry etching or by etching with hydrofluoric acid aqueous solution. The first mask layer is preferably an oxide layer. The structuring of the mask layer is carried out in two stages in order to selectively stop the etching on the first metallization layer. The mask layer is thus partially ablated in the first substep and completely ablated in the second substep by means of hydrofluoric acid gas phase etching, chemical-physical dry etching or etching with aqueous hydrofluoric acid in a selective manner until the first metallization layer. Preferably, the second metal layer is deposited in a layer sequence of tantalum and a thicker gold layer and structured with stopping in a sacrificial oxide.

According to a preferred embodiment, the formation of the vibratable structure is carried out by depositing and structuring a second mask layer, wherein, during the etching, the first metallization layer, the piezoelectric layer and the silicon functional layer are completely ablated in the vertical direction outside the etching mask defined by the second mask layer. The second mask layer is preferably also an oxide layer. The layer thickness of the second mask layer is preferably dependent on oxide degradation during the aluminum nitride etch and the silicon etch. Here, a lithography step is used, by means of which the entire layer stack is structured in the first region: oxide hard mask, thin gold electrode, aluminum nitride and silicon functional layer. This advantageously results in a maximum overlap of the piezoelectric layer with the two electrodes and thus in a maximum electromechanical efficiency of the resonator. Another advantage obtained by the oxide hard mask is a steeper etch angle during the structuring of the aluminum nitride and thus a better electrode overlap.

Preferably, the silicide layer is formed by deposition of platinum and nickel and subsequent thermal silicidation, wherein the thermal silicidation is in particular carried out at a temperature of 250 ℃ to 450 ℃.

Preferably, the structuring of the second metallization layer is performed by ion beam etching. It is particularly preferred that the ion beam etching is performed at an oblique angle of incidence, resulting in a downward etching of the first and/or second mask layer.

According to a preferred embodiment, the lateral fluctuations in the thickness of the piezoelectric layer 3 are reduced after deposition by an ion beam trimming process.

Another subject of the invention is a piezoelectric resonator produced by an embodiment of the method according to the invention.

Drawings

Embodiments of the invention are illustrated in the drawings and set forth in more detail in the description that follows.

Fig. 1 shows a resonator produced by means of an embodiment of the method according to the invention.

Figure 2 illustrates the steps of one embodiment of the method according to the invention.

Detailed Description

Fig. 1 shows a cross section (left) and a top view (right) of an embodiment of a resonator 1 according to the invention. The direction parallel to the main extension plane 10 of the device is also referred to below as the transverse direction, while the direction perpendicular thereto is described by the terms "upper" and "lower". The resonator 1 has a vibratable structure 9 consisting of a silicon body with a centrally arranged recess 24

9 is formed. The vibratable structure 9 is arranged above a substrate wafer 15 in which cavities 4 have been etched to expose resonators 1. The vibratable structure may here comprise a single movable body 9 or a plurality of movable bodies 9. The body 9 is formed by structuring a highly doped silicon functional layer 2 which is mechanically connected to the substrate 15 outside the vibratable structure 9 by means of a dielectric layer 16. A piezoelectric aluminum nitride layer 3 is arranged on the vibratable structure 9, by means of which the body 9 can be excited to vibrate. The deformation of the piezoelectric layer 3 is driven in this case by an electric field generated by means of two electrodes. The lower electrode is formed here by the silicon layer 2 of the body 9 itself, while the upper electrode consists of a thin metallization layer 7 which consists of a layer sequence of tantalum/platinum/gold/platinum/tantalum and is arranged on the piezoelectric layer 3 of the body 9. In order to electrically contact the two electrodes, the surface of the component has two bonding pads (bond pads) 22 and 23, the first of which is connected to the underlying portion 17 of the silicon layer 2 via a metal-silicon contact 6 and is in contact with the vibratable structure 9 via its anchor. The upper electrode, i.e. the gold layer 7, is connected to the second bonding pad 23 via a feed line 21, wherein a dielectric region 14 is arranged below the piezoelectric layer 3 and below the bonding pad 23, which dielectric region reduces the parasitic capacitance of the contact element 23. The

bonding pads

22, 23 and the supply lines 21 are each formed here by a thin metallization layer 7 and a thicker gold layer 8 arranged above it. In addition, the vibratable structure 9 has a thicker gold layer 8 of junctions in mechanically uncritical areasA structured layer (strukturrierte range) 18 to improve the conductivity accordingly.

As shown in fig. 2a, the starting point of the method according to the invention is a silicon layer 2 arranged on a wafer substrate 15 having a buried cavity 4 for a resonator 1. With respect to the main extension plane 10 (see fig. 1), three

lateral regions

11, 12, 13 can be distinguished, wherein the cavity 4 is arranged in the region 11, and a dielectric layer 16 is arranged in the

regions

12 and 13 between the substrate 15 and the functional layer 2, which dielectric layer 16 electrically insulates the silicon layer 2 from the substrate 15.

Then, as shown in fig. 2b, for the contact of the upper electrode, a dielectric oxide layer 14 is applied to reduce the parasitic capacitance. For this purpose, an isotropic silicon etch is first performed. The wafer is then thermally oxidized and the oxide is wet-chemically structured in such a way that it remains only in the recesses. The interaction of the silicon etch depth and the oxide thickness is here chosen such that the center of the spacer 23 is flush with the face of the silicon layer 2. The interaction of the mask, the isotropic silicon etch and the oxide etch and the etch down of the oxide mask are therefore selected here such that only a minimal surface shape remains at the transition from silicon 2 to oxide 14. This overhead for surface shape minimization is necessary in order to achieve as flat a surface as possible for the critical lithography techniques for resonator structuring.

As shown in fig. 2c, a piezoelectric layer 3 made of aluminum nitride is then deposited. Since this piezoelectric layer forms the active layer for the resonator 1, the layer properties have to be controlled very precisely in order to obtain a resonator 1 of high performance and also identical from part to part. An important variable in this case is the layer thickness, wherein the layer thickness fluctuations can advantageously also be reduced after the deposition by an ion beam trimming process.

Then, metal-silicon contacts 6 are fabricated (fig. 2 d). For this purpose, a sacrificial layer made of silicon oxide is first deposited. The purpose here is to collect the resulting and necessary over-etching of the metallization layer of the contact 6 in the sacrificial layer, rather than transferring it into the aluminum nitride layer 3, which is critical in terms of layer thickness variations. The sacrificial layer and the aluminum nitride 3 are then structured until into the silicon 2. After the contact hole structuring, a silicide former is deposited. Combinations of platinum and nickel have proven particularly suitable for this. The hot silicidation is performed in a process window between 250 ℃ and 450 ℃. Additionally, it is necessary to prevent gold from diffusing into the silicon 2. For this purpose, a barrier layer consisting of tantalum and tantalum nitride is subsequently deposited. The silicide layer stack and the barrier stack represent hard, mechanically strained layers which are not allowed to appear on the resonator structure and are thus removed around the contact hole 5. The oxide is removed very selectively with respect to the aluminum nitride by vapor hydrofluoric acid etching, chemical-physical dry etching or etching with aqueous hydrofluoric acid. Here, the requirements for the silicide layer and the barrier are: good electrical contact, adhesion to oxide, prevention of gold diffusion into the silicon, low layer thickness and stability to oxide etching, thermal stability of the electrical contact and thermal stability of the barrier to thermal stress in subsequent processes, such as wafer bonding.

Fig. 2e illustrates the deposition and structuring of the thin metallization layer 7. The metallization layer preferably consists of the layer sequence tantalum/platinum/gold/platinum/tantalum. The two thin tantalum layers are here adhesion layers to the underlying aluminum nitride 3 and to the subsequent second sacrificial oxide layer 19 (see fig. 2 f). Since the resonator 1 and thus the active aluminum nitride layer 3 are completely covered with the thin metallization layer 7, the metal structuring can here stop directly in the adjoining, non-critical aluminum nitride 3.

For the structuring of the second metal layer 8, the sacrificial oxide layer 19 is again required, since otherwise the second gold layer 8 cannot be structured selectively with respect to the first gold layer 7. The structuring of the sacrificial oxide layer 19 is two-stage (zweistrufig) (fig. 2 f). In the first structuring step, a dry chemical-physical etching is carried out, although not the entire layer 19 is ablated therein. Then, by means of a hydrofluoric acid gas phase etch, the material removal is stopped very selectively at the thin gold layer 7 in the second structuring step. Alternatively, the etching can also be carried out by means of a chemical-physical dry etching, in particular a Reactive Ion Etching (RIE), or etching with aqueous hydrofluoric acid, wherein the etching process has to be carried out such that a sufficient selectivity of the relatively thin gold layer 7 is given. A second metal layer 8 consisting of tantalum and a thicker gold layer is then deposited and structured to stop in the sacrificial oxide. For structuring, it may be advantageous, for example, to use ion beam etching at an oblique angle of incidence, thus resulting in a downward etching of the paint mask. The process and layer thicknesses are chosen such that the resulting surface shape of the second metallization layer 8 advantageously compensates for the critical lithography techniques used for resonator structuring. This includes: the second metal layer 8 is embedded in the sacrificial oxide 19. This is achieved by the choice of the layer thickness of the oxide layer 19, which is matched to the thickness of the second metal layer 8 and the etching removal. Additionally, the oxide etched edge is strongly rounded. The interaction of the masking, the etching of the sacrificial oxide layer and the structuring of the second metal layer 8 and the etching down of the metal mask 19 are selected such that only a minimal surface shape remains at the transition of the sacrificial oxide to the second metal layer 8.

As shown in fig. 2g, an oxide layer 25 is deposited again, this time with the function of a hard mask for resonator structuring. The layer thickness depends here on the oxide stripping during the aluminum nitride etching and the silicon etching. A single lithography step is used in order to perform the structuring of the entire layer stack: an oxide hard mask 25, a thin gold electrode 7, aluminum nitride 3 and a silicon functional layer 2. A maximum overlap of the piezoelectric layer 3 with the two electrodes is thus obtained for maximum electromechanical efficiency of the resonator 1. Another advantage that is derived from the oxide hard mask 25 is a steeper etch angle during the structuring of the aluminum nitride and thus again a better electrode overlap.

Finally, the sacrificial oxide 19, 25 is removed by means of hydrofluoric acid gas phase etching, dry chemical etching or etching with hydrofluoric acid aqueous solution, and the MEMS resonator 1 shown in fig. 2h is completed.

Claims

1. A method for producing a piezoelectric resonator (1), wherein a vibratable structure (9) of the resonator (1) is formed by a highly doped silicon functional layer (2), wherein the silicon functional layer (2) is arranged above a substrate (15) with respect to a vertical direction and has a transverse main extension plane (10) with a first, a second and a third transverse region (11, 12, 13), wherein a cavity (4) is arranged in the first transverse region (11) below the silicon functional layer (2), characterized in that the method has the following steps:

-depositing a piezoelectric layer (3) on said silicon functional layer (2),

-depositing a sacrificial layer of silicon oxide on said piezoelectric layer (3), and

-forming at least one recess (5) in the second lateral region (12) such that a face of the functional silicon layer (2) within the recess (5) is exposed, wherein the recess (5) extends in a vertical direction through the sacrificial silicon oxide layer and the piezoelectric layer (3),

-forming a silicide layer on the face of the silicon functional layer (2) exposed within the recess (5),

-forming a diffusion barrier layer on the silicide layer,

-removing said sacrificial layer of silicon oxide,

-depositing and structuring the first and second metallization layers (7, 8) on the piezoelectric layer (3) and the diffusion barrier layer, wherein a feed line (21) is formed by the structuring of the first and second metallization layers (7, 8), which feed line conductively connects the first and third lateral regions (11, 13), and a first connection element (22) is formed in the second lateral region (12) and a second connection element (23) is formed in the third lateral region (13) by the structuring,

-structuring the silicon functional layer (2) and the piezoelectric layer (3) such that the vibratable structure (9) is formed in the first lateral region (11), wherein the silicon functional layer (2) of the vibratable structure (9) is electrically conductively connected to the first connecting element (22) via the silicon functional layer (2) of the second lateral region (12) and forms a lower electrode of the resonator (1), which can be electrically contacted via the first connecting element (22), wherein the first metallization layer (7) of the vibratable structure (9) can be electrically contacted via the second connecting element (23) and forms an upper electrode of the resonator (1).

2. The method according to claim 1, wherein the piezoelectric layer (3) has aluminum nitride.

3. The method of claim 1 or 2, wherein the silicide layer has platinum and nickel.

4. The method of any preceding claim, wherein the diffusion barrier layer has tantalum and tantalum nitride.

5. Method according to one of the preceding claims, wherein the first and second metallization layers (7, 8) comprise gold, wherein the first metallization layer (7) in particular consists of a layer sequence of a thin tantalum layer, a platinum layer, a gold layer, a further platinum layer and a further thin tantalum layer, wherein the second metallization layer (8) in particular consists of a layer sequence of a tantalum layer and a gold layer.

6. Method according to one of the preceding claims, wherein, before the piezoelectric layer (3) is deposited, oxide regions (14) of the silicon functional layer (2) are formed in the third lateral region (13), wherein the second connection elements (23) are formed above the oxide regions (14) in such a way that the second connection elements (23) are shielded downwards by the oxide regions (14).

7. The method of claim 6, wherein the oxide region (14) is formed by:

-isotropically etching the silicon functional layer (2),

-thermally oxidizing said silicon functional layer (2),

-wet-chemically structuring the oxidized silicon functional layer (2) in such a way that the surface of the oxide partial region (14) and the surface of the non-oxide partial region extend flush.

8. Method according to any of the preceding claims, wherein the deposition and structuring of the first and second metallization layers (7, 8) is carried out in the first lateral region (11) such that the first metallization layer (7) completely covers the face of the piezoelectric layer (3) and the second metallization layer (8) is structured such that the second metallization layer covers one sub-region (18) of the first metallization layer (7) and does not cover the other sub-region of the first metallization layer (7).

9. Method according to any of the preceding claims, wherein the structuring of the second metallization layer (8) is performed by:

-depositing a first mask layer (19),

-subjecting the first mask layer (19) to a chemical-physical dry etch, wherein the first mask layer (19) is only partially ablated in a vertical direction,

-etching the first mask layer (19), wherein the first mask layer (19) is completely ablated in a vertical direction, wherein the etching of the first mask layer (19) is performed by hydrofluoric acid vapor etching, chemical-physical dry etching or etching with hydrofluoric acid aqueous solution.

10. Method according to one of the preceding claims, wherein the formation of the vibratable structure (9) is performed by depositing and structuring a second mask layer (25), wherein, upon etching, the first metallization layer (7), the piezoelectric layer (3) and the silicon functional layer (2) are completely ablated in a vertical direction outside an etching mask defined by the second mask layer (25), wherein the etching of the second mask layer (25) is performed by hydrofluoric acid gas phase etching, chemical-physical dry etching or by etching with aqueous hydrofluoric acid.

11. Method according to any one of the preceding claims, wherein the silicide layer is formed by deposition of platinum and nickel followed by thermal silicidation, wherein the thermal silicidation is in particular carried out at a temperature of 250 ℃ to 450 ℃.

12. Method according to any of the preceding claims, wherein the structuring of the second metallization layer (8) is performed by ion beam etching.

13. The method according to any of the preceding claims, wherein after deposition, the lateral fluctuations in the thickness of the piezoelectric layer (3) are reduced by an ion beam trimming process.

14. A piezoelectric resonator (1) manufactured according to the method of any one of the preceding claims.